Scheduling Optical and Lens Manufacturing Around Coating Chambers

An optical lab lives or dies on its coating chambers, and the only schedule that reflects reality is one that treats each chamber as a single run per day, pools the interchangeable polishers, and works backward from every prescription ship date. EDGEBIC by User Solutions models the chamber as a one-job-per-day work center, expands a pool of polishers into whichever machine finishes soonest, and flags the jobs that cannot make their promised day while there is still a shift left to act.

Lens production is a strange mix. The volume looks like a flow shop, the due dates look like a job shop, and the constraint is a vacuum chamber whose loading behavior no hours-per-day model describes correctly.

Why Chamber Hours Are the Wrong Unit

A coating chamber does not fill up like a mill. You load it, pump it down, run the recipe, vent it, and unload it. Whether the recipe takes ninety minutes or four hours, the chamber is committed for that cycle and often for the balance of the shift once the technician has set the sources.

A scheduler that sees a sixteen-hour daily capacity will happily place four separate jobs on one chamber in one day. The floor cannot do that. The fix is a one-job-per-day rule on the work center: each chamber unit accepts a single job per day, and the next job goes to a second chamber or to tomorrow. If you run three chambers, you have three slots a day, and the schedule says so plainly.

This is the same modeling pattern that heat treat and cure work uses, described in heat treating furnace scheduling. The chamber is a batch resource whose unit of capacity is the run, not the hour.

Pooling the Polishers Instead of Naming One

Surfacing and polishing is the opposite problem. You have eight or twelve machines that can do the same job, and the routing names exactly one of them because that is how it was written years ago. Every job then queues behind every other job on that named machine while three identical machines sit idle.

Bind the routing step to a work center group instead. At schedule time the engine expands the group into its member machines, compares each member's projected finish against live load, and places the job on the one that gets it done first. Members can carry their own efficiency factor, so a newer machine that runs a job in 0.8 of the standard time is modeled honestly rather than assumed equal. The general mechanics are covered in routing a job to a backup machine when the primary is full.

Jobs already started stay on the machine that is running them. Only work that has not begun re-shops the pool on the next reschedule.

Sequence-Dependent Changeovers on the Chamber

Not all coating transitions cost the same. Going from one anti-reflective stack to a similar one may cost twenty minutes of recipe change. Going from a hard coat to a mirror stack can mean changing sources and a long conditioning run. A single flat setup number on the routing step averages both and is wrong in both directions.

A per-chamber setup matrix carries the real changeover hours from one coating family to the next. The scheduler looks up the transition from the job that just ran to the job it is about to place and applies that number, not the average. Group your recipes into a handful of families and the matrix stays small enough to maintain: eight families give you sixty-four cells instead of thousands of part-to-part entries. The concept is explained in sequence-dependent setup times, and the family shortcut in how setup families reduce scheduling complexity.

Once the matrix exists, the sequence optimizer can group compatible recipes to shrink total changeover time on the chamber rather than accepting whatever order the due-date sort produces. The multi-run layer is guaranteed never to return a schedule worse than the baseline it started from, so running it costs you nothing but the time it takes.

Backward From the Ship Date

Most lab work carries a hard courier day. Forward scheduling from now tells you when a job could finish. Backward scheduling from the ship date tells you when each step has to start and whether the calendar has room. That second answer is the one you can staff against.

The engine places each job's steps backward from its due date onto finite capacity. Jobs that fit are confirmed. Jobs that do not are flagged as at risk, with the step that could not be placed identified. See forward versus backward scheduling for the underlying trade-off and high-mix low-volume job shop scheduling for the pattern a lab shares with short-run shops.

A Worked Day

Twelve jobs need coating, two chambers are available, and one job is a mirror stack.

The mirror stack is flagged Tuesday morning, not Wednesday afternoon. The planner either moves it ahead of the hard coat to shorten the transition, adds a Wednesday evening window on Chamber B, or calls the account about Thursday. All three options exist because the flag arrived a day early.

Tracking What Actually Ran

Chamber cycles rarely match the standard exactly. Operators can log start, stop, and quantity at a shop floor station, and those actuals flow back into the plan. Completed runs are never moved by a later reschedule: what happened stays recorded, and only the unfinished work reflows. Over a few weeks the logged chamber times tell you which recipes are consistently over their standard, which is the input your setup matrix needs to get better.

Heritage in Batch-Constrained Work

User Solutions has built finite capacity scheduling since 1991, more than 35 years, for operations where a single constrained resource sets the pace: US Navy, GE, BAE Systems, and Cummins across 33 locations. The lineage behind EDGEBIC, including the RMDB heritage, drove GE Railcar on-time delivery from 30 percent to 90 percent and handled the Nimitz refit at more than 26,000 tasks. An optical lab scheduling two chambers against 400 promises a day is the same discipline at a different scale.

Where to Start

Flag your chambers as one job per day, put your interchangeable polishers into one group, define three or four coating families with real changeover hours between them, and schedule backward from tomorrow's courier. The first honest at-risk flag pays for the setup.

For the fundamentals, what is production scheduling is the plain-language start. The industry fit guide maps neighboring sectors and EDGEBIC is the product hub. Ready to see how many chamber slots you really have? Contact US for a demo.